1992 buick lesabre problem with shaking?

1992 or 93 buick leSabre 3800 engine. start up it shakes (vibrates) and when driving poor acceleration and more shaking. Popped the hood and heard a hissing noise towards the back of the engine close to steering pump res.; somewhere along back side of engine.....any clues as to why it shakes and what hose is causing the hissing noise?